The data writing method of MRAM is to use two wirings (Bit Line and Write World Line) to induce the cell interconnected by the magnetic field, in order to change the magnetoresistance value of the memory layer by changing the direction of the magnetization state of the magnetic material of the memory layer. Thus, when reading the memory information, uses the reading of the resistance value generated by flowing the current into the selected magnetic memory cell to judge the bit value of the memory information.
Referring to TW Patent No. 583666, it discloses a method to switch a magnetoresistive memory device by providing a magnetoresistive memory element close to a first conductor and a second conductor, wherein the magnetoresistive memory element includes a first magnetic region and a second magnetic region, and these two regions are divided by a tunneling barrier. At least one of the first and second magnetic regions comprises N ferromagnetic material layers that are antiferromagnetically coupled. N is an integral number equal or greater than two, and every single layer has an adjusted magnetic moment to provide a data writing mode. Every first and second magnetic region has a magnetic moment vector close to the tunneling barrier: at time t0, it is oriented in a preferable direction; at time t1, it is connected to a first current flowing through the first conductor; at time t2, it is connected to a second current flowing through the second conductor; at time t3, it cuts the first current flowing through the first conductor; at time t4, it cuts the second current flowing through the second conductor and this makes the magnetic moment closing to the tunneling barrier positioned in a direction different to the initial preferable direction at time t0.
Conventional magnetoresistive memory device uses toggle mode to increase the data writing selectivity, in order to push the magnetoresistive memory close to the mass production stage. Referring to FIGS. 14A, 14B, 14C, 14E and 14E, they are the schematic views showing the time sequence and the data writing mode of the conventional magnetoresistive memory device according to the embodiment. The magnetoresistive memory applies a word current 30 and a bit current 40 to the magnetic field to cause a throughput of the magnetic field to rotate the effective magnetic moment vector of the magnetoresistive memory device 180 degree. However, because of the disturbance from the exposed magnetic field, the initial direction of the magnetoresistive memory device at time t0 is often being deflected and sometimes causing data writing error. Therefore, the magnetoresistive memory device disclosed from the patent mentioned above uses a negative current to flow through before data writing, in order to deflect the magnetoresistive memory back to the correct initial direction at time t0 to resolve the disturbance from the exposed magnetic field, and hence increases the ratio of the correct data writing.
Although the magnetoresistive memory has advantages of non-volatility, high density, fast read/write and high endurance, but because of the especial toggle mode, a larger data writing magnetic field is required. Therefore, it is easy to cause a larger data writing current and increases the difficulty to match with other peripheral devices. However, although the switching method for the magnetoresistive memory mentioned above can reduce the data writing current and increase the magnetoresistive memory's correct data writing rate, but how to generate the forward and backward current mentioned in this method has become a problem for the related researchers.
Therefore, how to develop a memory structure with a simple structure, a fixed current, and is able to generate the forward and backward current has become an urgent problem for the related researching field.